PROJECT SUMMARY Episodic memory, or the ability to remember past events with specific detail, is central to the human experience and is related to learning and adaptive functioning in a variety of domains. In typically developing children, episodic memory improves emerges during infancy and improves during early childhood and beyond. Despite remarkable early episodic memory skills, most early recollections are lost to infantile amnesia, individuals' inability to recall events occurred in the first 2 or 3 years of life. Developmental processes within the hippocampus are hypothesized to be primarily responsible for both the early emergence of episodic memory in children and the loss of early recollections due to infantile amnesia. However, these hypotheses are based on non-human models and in-vivo investigations in early human development have been significantly limited by the methodological challenge of acquiring neuroimaging data, particularly task-related functional neuroimaging data, from young children. Recent studies in adults have highlighted that the hippocampus is involved in the acquisition of the initially arbitrary association between new words and their referents, a capacity markedly impaired in hippocampal amnesia. We propose to leverage the remarkable word-learning skills in infants and toddlers to explore whether neural substrates of memory for words can be used as a marker of early episodic memory. The proposed research will explore new methods to test hippocampal structure and function in infants and toddlers ages 18 to 30 months, a period during which episodic memory improves, hundreds of words are being learned, but infantile amnesia operates. Relevance to Public Health: Healthy episodic memory provides a foundation for the emergence and development of autobiographical memory, continuity of self from past to future, and is associated with intellectual ability and academic achievement. The development of episodic memory is impaired following even mild forms of acquired neurological insult, mental health conditions such as anxiety and depression, and neurodevelopmental disorders; language acquisition is additionally impaired in a number of disorders underscoring that a characterization of memory and vocabulary development is key to understanding adaptive functioning in various populations of children.